This invention relates to a head for recording in and reproducing from a semiconductor recording medium which can be electrically rewritten an information signal through an electrode stylus which relatively slides on that medium.
A method is known whereby an information signal, e.g., a video signal and an audio signal is arbitrarily recorded and reproduced with high density using a recording medium consisting of a semiconductor. This method is disclosed in U.S. Pat. No. 4,340,953. The recording medium comprises a semiconductor substrate consisting of, e.g., monocrystal Si and an insulation film which is formed on this semiconductor substrate and has a charge storage function. The above insulation film is a double-layer film consisting of a SiO.sub.2 film and a Si.sub.3 N.sub.4 film formed on this SiO.sub.2 film. A conductive recording and reproducing head moves relatively on this recording medium. A signal voltage is applied through the head in the direction of a thickness of the recording medium, so that the signal charges are stored in the insulation film. On the other hand, the depletion layer is formed in the semiconductor substrate in response to the signal charges stored. By detecting the electrostatic capacity in the direction of a thickness of the recording medium due to this depletion layer by means of the recording and reproducing head which moves relative to the recording medium, the stored information is reproduced.
The reproducing stylus of the pickup to be used for a video disc of the electrostatic capacity type is constituted as disclosed in, for example, a Japanese Patent Laid-open Application 56-58147 and 56-134333. The recording and reproducing head to be used for the recording and reproducing method using a semiconductor recording medium is also constituted in the same manner as the reproducing stylus to be used for the above-mentioned electrostatic capacity type video disc, i.e., an electrode stylus is attached to the side surface of an electrode supporting substrate. However, different from the reproducing stylus of the electrostatic capacity type video disc, the electrode stylus of this kind is also used as a recording stylus and a signal voltage is applied to the stylus when recording information. As described above, since their use methods are quite different, it was found that such an electrode stylus has the following peculiar problems that were not caused for the reproducing stylus for the electrostatic capacity type video disc.
(1) Since the electrode stylus slides on the recording medium which rotates at a high speed, an excellent wear resistance is required. On the contrary, when the hardness of the electrode stylus is higher than that of the recording medium, the recording medium will have been damaged. This is because the semiconductor recording medium is harder and has a less elasticity as compared with the electrostatic capacity type video disc. If a hard stylus such as diamond like a conventional reproducing stylus for electrostatic capacity type video discs is used for the electrode supporting substrate, the electrode stylus will float over the surface of the recording medium and the preferable contact relation will not be provided since the abrasion of the electrode stylus is larger than that of the supporting substrate. In the method using a semiconductor recording medium, since a signal voltage is applied through the electrode stylus and the recording is performed, it is an inevitable requirement to secure the excellent contact relation between the electrode stylus and the recording medium in order to improve the recording performance. A poor contact relation will adversely disable the recording and reproduction of images.
(2) In the recording and reproducing method using a semiconductor recording medium, while a voltage is applied to the electrode stylus to record a signal, a fairly large current of 100 A/cm.sup.2 or more flows, causing the Joule heat to be produced. Furthermore, since the electrode stylus slides on the recording medium or disc which rotates at a high speed of, e.g., 1800 rpm, the frictional heat is also produced. Hence, a large amount of thermal and mechanical load is applied to the electrode stylus. Thus, the electrode stylus may be easily peeled from the electrode supporting substrate due to a difference in thermal expansion coefficient between the electrode stylus and the electrode supporting substrate, mechanical vibration to which the electrode is subject, and sliding friction.
The film forming the electrode stylus may be thickened to diminish such thermal and mechanical load to be applied to the electrode stylus and to prevent the electrode stylus from being broken. However, to maintain the resolution of the information signal which is recorded and reproduced to be a predetermined level or more, a thickness of the film of the electrode stylus must be 0.5 .mu.m or less.